Antifriction bearings are conventionally utilized to support spindles for high speed rotation that is necessary with certain industrial machines as well as with other uses. For example, certain grinding wheelheads have spindles that support grinding wheels for grinding internal bores and the diameter of the grinding wheels thus cannot be varied to provide the requisite cutting speed for giving good surface finish. As such, only the rotation of the wheelhead spindle can be increased to provide higher cutting speeds at the interface of the grinding wheel and the workpiece. In certain instances, this spindle speed must be as great as about 150,000 revolutions per minute. In order to provide the high speed rotation, it is necessary to axially preload the spindle so that the ball elements of antifriction bearings which support the spindle will track in a true circle to prevent vibration that can cause heat and ultimate bearing failure.
Spring loaded ball slides are conventionally utilized to mount one of the antifriction bearings that support a high speed spindle and to axially preload the spindle through such bearing. These slides conventionally have an annular shape and one end which supports the outer race of the antifriction bearing. Balls which ride in axial grooves on the slide and in associated axial grooves in a support housing are utilized to radially position the slide. A spring biases the other end of the slide so as to axially bias the outer race of the antifriction bearing with respect to the inner race in order to provide the axial preloading that permits high speed spindle rotation. Axial preloading of the slide mounted bearing also axially biases the spindle so that an antifriction bearing which supports its other end is likewise preloaded to permit the high speed spindle rotation.
With ball slide mounted spindles, the machining of the slide and housing grooves that receive the balls for supporting the slide must be extremely precise so as to maintain the axis of spindle rotation in a fixed location. If the axis of spindle rotation is not maintained in a fixed location, the wobbling that takes place, even if very slight, can cause vibration that builds up heat and causes bearing failure. Thus, the spacing between the housing and slide grooves upon the initial machining cannot be too great or the radial location of spindle rotation will not be fixed and bearing failure will result. If there is an interference fit between the balls and the grooves, the biasing spring may not have a sufficient force to move the slide and thereby provide the preloading of the antifriction bearings that support the spindle. Even if the machining is precise so that there is no clearance and no interference between the balls and the grooves, heat which builds up during the high speed rotation can cause thermal expansion that deforms the balls and/or the grooves so as to result in a loose fit that allows wobbling of the axis of spindle rotation and the possibility of bearing failure.
Also, U.S. Pat. No. 3,939,944, which is assigned to the assignee of the present invention, discloses an oil-mist lubrication system for lubricating antifriction bearings with an oil-mist lubricant in order to prevent bearing failure.